1. Field of the Invention
The present invention relates to a photosensitive lithographic printing plate and more particularly, the invention relates to a lithographic printing plate having a photosensitive layer of a novel and improved photosensitive diazo-oxide resin.
2. Description of the Prior Art
It is well known to use a photosensitive diazo-oxide in the production of photocopies or photoresists and also as a photosensitive material for lithographic printing plates. In these techniques, as the result of light exposure, due to the properties of the photosensitive diazo-oxide, a difference in solubility between the exposed areas and the unexposed areas results and by treating the exposed layer of such a material with an appropriate solvent, a desired image portion remains on the support while undesired portions are washed away from the support. These techniques are described in detail in the specifications of, e.g., U.S. Pat. Nos. 3,046,121, 3,046,122, and 3,046,123. In the above patents, the ester or acid amide of benzenediazo-oxide or naphthalenediazo-oxide is used as the photosensitive material for photosensitive lithographic printing plates. Other various materials for this purpose have also been reported.
However, almost all of these components are low molecular weight compounds and when such a compound is used individually for a photosensitive lithographic printing plate, crystallization occurs, which results in a poor film of the compound being obtained, and thus the image formed has low mechanical strength. This makes it difficult to obtain many satisfactory copies or prints. Therefore, the aforesaid photosensitive material is frequently used together with an alkali-soluble resinous binder or as a compound formed by the reaction thereof with an alkalisoluble resinous material.
Such polymers are described in the specifications of U.S. Pat. No. 3,046,120, British Pat. No. 1,113,759, and U.S. Pat. Application Ser. No. 684,636, filed on Nov. 21, 1967 now abandoned. The compounds described in these specifications are mainly polymers such as phenol resins and aminostyrene resins.
However, although these compounds may have good sensitivity and provide sufficient difference in solubility between the exposed areas and the unexposed areas, they have the disadvantages that coated layers of these compounds are brittle and have a comparatively poor flexibility.